1. Field of the Invention
The present invention relates generally to an inflator device including gas generators and more specifically to a dual level inflator which can selectively release gas at different rates and levels and thus enable an air bag or the like type of inflatable safety restraining device, to be deployed at different output levels in accordance with different sensor inputs.
2. Description of the Related Art
Recently, there has been a demand for controlling the rate and amount of inflation of safety devices such as air-bag restraint systems, in accordance with variables such as passenger size, position, seat belt usage and the velocity of a vehicle at time of collision.
In order to provide optimal occupant protection, different levels of output are required from the air bag inflator. For example, in a high speed collision with a large unbelted person, full rapid inflation of the air bag is required to provide the best restraint. In lower speed crashes with smaller size occupants or even out-of-position occupants, a lower, slower rate of inflation is required so as not to inadvertently injure the occupant but still provide enough inflation to provide restraint.
In order to achieve the two levels of inflation, it has been proposed in U.S. Pat. No. 3,773,353 to Trowbridge et al. to provide two separate charges and to ignite one in the event that a slow inflation is required and to ignite both in the event of a high speed collision, thus achieving the very rapid inflation and deployment of the air bag which is necessary under such circumstances. In this device the charges are arranged within a reservoir which is filled with a non-toxic gas under pressure. This housing is sealed by a burst plate that is punched out by a piston and rod type of arrangement when a first of the two charges is detonated. This arrangement however, suffers from the drawback of being relatively complex and therefore, relatively expensive. For example, no less than three burst plate arrangements are necessary. Also, the charges are each isolated from the reservoir and reservoir gas by an inner housing and a respective rupturable closure.
U.S. Pat. No. 3,905,515 to Allemann discloses another two-stage inflator assembly which utilizes two separate charges and which disposes the charge in a chamber which is used to store a non-noxious gas under pressure. However, this arrangement is even more complex than that in U.S. Pat. No. 3,773,353. In this arrangement a portion of the burst disc forms the head of a slidable shuttle valve member which is projectable into an exhaust passage to partially throttle the outflow of gases following a detonation of one or both of the two charges.
Consequently, there is a need for a cost effective, light-weight, compact, simple multi-level inflator for air bags and the like.